Should we wrap the sdev->device_busy read and test in a new
scsi_device_busy(), so as to preserve the old polarity?
Reviewed-by: Venkatesh Srinivas <venkateshs@xxxxxxxxxx>
On 8/11/14, Jens Axboe <axboe@xxxxxxxxx> wrote:
> On 2014-08-10 06:54, Guenter Roeck wrote:
>> The latest kernel fails to boot qemu arm images when using scsi
>> for disk access. Boot gets stuck after the following messages.
>>
>> brd: module loaded
>> sym53c8xx 0000:00:0c.0: enabling device (0100 -> 0103)
>> sym0: <895a> rev 0x0 at pci 0000:00:0c.0 irq 93
>> sym0: No NVRAM, ID 7, Fast-40, LVD, parity checking
>> sym0: SCSI BUS has been reset.
>> scsi host0: sym-2.2.3
>>
>> Bisect points to commit 71e75c97f97a ("scsi: convert device_busy to
>> atomic_t"). Code inspection shows the following suspicious change
>> in scsi_request_fn.
>>
>> out_delay:
>> - if (sdev->device_busy == 0 && !scsi_device_blocked(sdev))
>> + if (atomic_read(&sdev->device_busy) &&
>> !scsi_device_blocked(sdev))
>> blk_delay_queue(q, SCSI_QUEUE_DELAY);
>> }
>>
>> 'sdev->device_busy == 0' was replaced with
>> 'atomic_read(&sdev->device_busy)',
>> meaning the logic was reversed. Changing this expression to
>> '!atomic_read(&sdev->device_busy)' fixes the problem.
>>
>> Cc: Christoph Hellwig <hch@xxxxxx>
>> Cc: Hannes Reinecke <hare@xxxxxxx>
>> Cc: Webb Scales <webbnh@xxxxxx>
>> Cc: Jens Axboe <axboe@xxxxxxxxx>
>> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
>> ---
>> drivers/scsi/scsi_lib.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index 9c44392..ce62e87 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -1774,7 +1774,7 @@ static void scsi_request_fn(struct request_queue
>> *q)
>> blk_requeue_request(q, req);
>> atomic_dec(&sdev->device_busy);
>> out_delay:
>> - if (atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev))
>> + if (!atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev))
>> blk_delay_queue(q, SCSI_QUEUE_DELAY);
>> }
>>
>>
>
> That's a no-brainer obvious fix!
>
> Acked-by: Jens Axboe <axboe@xxxxxx>
>
>
> --
> Jens Axboe
>
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